Virus Transmission

Abstract

The secondary spread of the seed-transmitted virus diseases both in the field and glass houses takes place through different vectors. Under field conditions, the infected seedlings raised from virus-infected seeds act as primary foci of infection and further spread takes place through insect vectors. Transmission through mite and insects is a natural and main method of virus spread, and the major vectors of viruses are from the phylum Arthropoda (94%) and other important vectors (about 6%) are nematodes (Phylum: Nematoda). Nearly 35 seed-transmitted viruses are from Potyvirus group, which have aphid vectors. The next highest seed-transmitted viruses (28) are found in Nepovirus group, in which nematodes are the vectors. Even beetle-transmitted seed-borne viruses are found in Fabavirus group (3) and Sobemovirus group (5). Soil-borne fungal vectors have also transmitted 4 and 2 viruses in Furovirus and Necrovirus groups. While dealing with the insect vector transmission, the virus--vector relationship of some of the seed-transmitted viruses was also discussed. Doubtful reports of seed transmission of certain viruses by whiteflies and mites are to be confirmed by further studies. Information on role of pollen in seed transmission is discussed. Potexvirus and Tobamovirus groups, which are externally seed-borne in certain solanaceous crops, were also presented.